Exhibit 99.1

                CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350,

                             AS ADOPTED PURSUANT TO

                  SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

         In connection with the Annual Report of the Penwest Pharmaceuticals Co.
Savings Plan (the "Plan") on Form 11-K for the period ended December 31, 2002 as
filed with the Securities and Exchange Commission on the date hereof (the
"Report"), the undersigned, Tod R. Hamachek, Chief Executive Officer of Penwest
Pharmaceuticals Co. hereby certifies, pursuant to 18 U.S.C. Section 1350, that,
to the undersigned's knowledge:

         (1) the Report fully complies with the requirements of Section 13(a) or
15(d) of the Securities Exchange Act of 1934; and

         (2) the information contained in the Report fairly presents, in all
material respects, the financial condition and results of operations of the
Plan.

                                                     /s/ Tod R. Hamachek
                                                     ---------------------------
Dated: June 26, 2003                                 Tod R. Hamachek
                                                     Principal executive officer

A signed original of this written statement required by Section 906, or other
document authenticating, acknowledging, or otherwise adopting the signature that
appears in typed form within the electronic version of this written statement
required by Section 906, has been provided to the Plan and will be retained by
the Plan and furnished to the Securities and Exchange Commission or its staff
upon request.